Heat pump control



June 1, 1965 w. w. BELL, JR

HEAT PUMP CONTROL Filed May 18. 1961 FIG. I

FIG. 2

INVENTOR.

WILLIAM W. BELL JR. BY

ATTORNEY.

United States Patent '0 3,186,477 HEAT PUMP CONTROL William W. Bell, Jr., Marcellus, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware- Filed May 18, 1961, Ser. No. 116,928 6 Claims. (Cl. 1652) This invention relates broadly to air conditioning apparatus, and more particularly, to air conditioning apparatus employing a refrigeration system operable under the reverse cycle principle. Apparatus of this type are generally known as heat pumps and are operable to supply either cooled or warm air to an area to be treated.

In one common commercial self-contained heat pump, a partition within the heat pump casing separates the casing into an indoor compartment and an outdoor compartment. The components of the refrigeration system are normally arranged so that the outdoor heat exchange coil and the compressor are in the outdoor compartment and the indoor heat exchange coil is in the indoor compartment. The fan for passing air over the indoor coil and the fan for passing air over the outdoor coil are driven from a single motor Within the casing.

When the refrigeration system has its cycle reversed from cooling to provide heating, it is sometimes incapable of providing adequate heating in regions where low ambient temperatures are encountered. Consequently, one or more electric resistance heaters are built into the air conditioning apparatus and are selectively utilized to sup plement the heating capacity of the refrigeration equipment itself, as required.

When the air conditioning apparatus is used on the cooling cycle, the heat exchange coil which is located outdoors function as the condenser and the heat exchange coil which is located indoors function as the evaporator.

On the heating cycle, the functions of the coils are re versed; the heat exchange coil which is located indoors functions as the condenser and the heat exchange coil which is located outdoors functions as the evaporator.

During heating operation, the outdoor heat exchange coil often becomes coated with an insulating layer of frost which impedes the efliciency of the refrigerating systerirli by reducing the heat transfer characteristics of this co A common method for removing the coating of frost from the outdoor heat exchange coil in the heat pump is to reverse the refrigerant =flow so that the unit temporarily reverts to cooling cycle operation. The operation of the fan for passing air over the outdoor coil is terminated to speed up the defrost cycle. As both the indoor fan and outdoor fan are driven from a common motor, the indoor fan is also stopped. However, the resistance heaters, which are usually positioned adjacent the indoor coil so that the indoor fan will cause air which is to be heated to flow through the indoor coil and over the heaters, will remain energized. The fan motor may remain off a sufficient time so that the auxiliary resistance heaters might create a fire hazard because the heat produced cannot be adequately dissipated. A fusible link has been used to protect the electric resistance heaters. However, upon overheating the link burns out and must be replaced. Until the link is replaced, the resistance heaters are inoperable.

An object of this invention is to provide a heat pump having an auxiliary heater with an improved control means for such auxiliary heater so as to overcome the objections and disadvantages in prior constructions.

Another object of this invention is to provide a heat pump having an auxiliary heater with an improved control for energizing and deenergizing the auxiliary heater in response to predetermined conditions within the refrigeration system of such heat pump.

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Another object of this invention is to provide an air conditioning apparatus having a reverse cycle refrigeration system and employing an electric resistance heater with an improved control for the electric resistance heater operable in response to predetermined temperatures of the refrigerant in a line in the refrigeration system connecting the reversing valve with the outdoor heat exchange coil.

It is a further object of this invention to provide an improved method for controlling the operation of a resistance heater used with a heat pump. Other objects and advantages of this invention will become readily apparent hereafter.

The present invention relates to an air conditioning apparatus of the type including a refrigeration system which is selectively operable to cool or heat the air. The refrigeration system includes a compressor, a reversing valve,

an outdoor coil, expansion means, and an indoor coil connected to form a reverse cycle refrigeration system. A resistance heater, adapted to be connected to a source of electric current, is provided to supply supplementary heat at low outdoor ambinet temperatures when it may be necessary to supplement reverse cycle heat. The control for the air conditioning apparatus comprises means for energizing the resistance heater in response to a first predetermined temperature of .the refrigerant in the connection between the reversing valve and the outdoor coil and for deenergizing the resistance heater in response to a second predetermined condition of the refrigerant in the connection between the reversing valve and the outdoor coil.

This invention further relates to a method of controlling the operation of the auxiliary heater used wit-h a heat pump having a reverse cycle refrigeration system comprising a compressor, a reversing valve, an outdoor coil, expansion means and an indoor coil, the method comprising the steps of: energizing the auxiliary heater in response to a first predetermined temperature condition of the refrigerant in a connection to the outdoor coil and deenergizing the strip heater in response to a second predetermined temperature condition in the connection to the outdoor coil.

The present invention will be more fully understood when the following specification is read in conjunction with the accompanying drawing wherein:

FIGURE 1 is a schematic diagram of the air conditioning apparatus which includes a reverse cycle refrigeration system; and

FIGURE 2 is a schematic Wiring diagram of the electrical circuitry which is used to control the air conditioning apparatus of FIGURE 1.

Referring more particularly to FIGURE 1, there is shown for the purpose of illustrating this invention, a self-oontained air-to-air type heat pump employing a refrigeration system operable under the reverse cycle principle. In apparatus of this type, a first heat transfer coil is disposed within the area to be treated and a second coil is located outside the area. to be treated, usually in the ambient.

The heat pump includes a casing 5 adapted to be mounted in an aperture or Window in the Wall of an area to be conditioned. The casing is divided by partition 6 into two separate compartments hereinafter designated indoor compartment 7 and outdoor compartment 8.

A compressor 10 discharges relatively hot gaseous refrigerant through discharge line .11 to the fouraway reversing valve 12, which is employed for the purpose of reversing refrigerant fiow through .a portion of the system in order .to obtain the desired heating and cooling effects. From the reversing valve 1 2, which is controlled by the operation of the solenoid in a manner livered over the coil by fan 19.

the heat exchange coils in the refrigeration system. In

the indoor coil, refrigerant is converted to vaporous refrigerant as it extracts heat from the stream of air de- Vaporous refrigerant so formed .fiows through line 17 to reversing valve 12 from whence the refrigerant flows through suction l ne 1-8 into the compressor to complete the refrigerant flow cycle.

The fan 19 may be driven from an electric motor suitably mounted within casing 5.

The motor as may have a double-ended shaft, upon the opposite ends of which are mounted fans 1% and 21.

As is conventional in heat pump systems of the type described, the four-way reversing valve may be actuated so that line 1:1 is placed in communication with the in door coil 16 and line 18 is placed in communication with outdoor coil 14 when it is desired to operate the unit on a heating cycle. Under these circumstances, heat from .the refrigerant flowing in coil 16 is rejected to the air within the area to be treated. The rejection of heat from the refrigerant converts the gaseous refrigerant to liquid refrigerant which flows through expansion means 15 to outdoor coil 14, which new functions as an evaporator. The vapor ous refrigerant created in outdoor coil 14 as a result of heat transfer between the refrigerant and the ambient air flows through the reversing valve into suction line 18.

As noted above, the refrigeration system may be incapable of providing sufficient heat to the area to be treated, especially when it is used in geographical areas which are subject to low outdoor ambient temperatures. A resistance heater 22, which consists of a suitable high resistance wire through which current is adapted to be selectively passed is used to provide auxiliary heat. Thus the air which is heated to a certain degree by being induced through heat exchange coil 16 by fan 19 is further heated by being forced over resistance heater 22 by the fan 19.

The novel control means 23 for energizing and deenergizing strip heater 22 comprises a temperature actuated switch 24 which is movable in response to the temperature in line 13. One means of actuating the switch is a bellows member 25 operable in response to the temperature sensed by capillary bulb 26 which is in heat exchange relationship with line 13.

It can readily be appreciated that the above described system has particular utility in a window type room air conditioner as illustrated, but is not limited thereto. When used as a window type unit, the compartment 7 within which the indoor coil is disposed faces the area to be treated and the compartment 8 within which the outdoor coil is disposed faces the ambient.

The electrical control circuitry for the system of FIG- URE 1 is shown in FIGURE 2. A suitable source of alternating current (not shown) is adapted to supply current via leads L1 and L2. It will be understood, of course, that the system can operate on three-phase current if it is suitably modified.

The control circuit comprises a manual selector switch 30, a room thermostat 31, a thermostat control 23 for strip heater .22, solenoid 42 for actuating reversing valve 12, defrost control means it, compressor motor 45, and fan motor 2%.

The manual selector switch 30 comprises two switch arms, 32 and 33. The switch arm 32 is movable between the solid line position shown wherein automatic operation of the fan and refrigeration system is maintained to the dotted line position wherein manual control of the .fan motor 20 is permitted.

Switch arm 32 may be placed in the dotted line position when it is desirable to operate fan motor 20 to merely circulate air when the refrigerating system is not in operation. Thus a circuit is completed from line L1 through switch arm 32, line :34, line 35, fan motor 20, line 3 6 to lead L2, energizing fan motor 2d.

Switch arm 33 controls the speed of operation of fan motor 26 when switch arm 32 is in the solid line position. When the switch arm 33 is in the solid line position shown, the fan operates under high speed conditions, when switch arm 33 is in the dotted line position, the fan operates under low speed.

The room thermostat 311 comprises two single pole double-throw switches 40 and 4 1. Switches to and 41 may each comprise bimetallic elements. Switch 41 is responsive to predetermined temperature values which are higher than the temperature values to which switch so is responsive.

When solenoid 4-2 is deenergizcd, the reversing valve is in the cooling position. .Upon cnergization of solenoid t2, the reversing valve is moved to the heating position. In series with the solenoid 42 is defrost control means 44 which may be a Ranco D-SO or D-52 control. The operation of this control is based on the increase in the difference in temperature between the outside coil and the outside ambient air when ice is formed on the outside coil as compared with normal clear coil conditions.

When the heat pump is operating on the cooling cycle, the switch arm 32 of manual selector switch 30 is in the position shown in solid line. The switch arm 33 of selector switch 30 may be set in the high position as illustrated by the solid line. A circuit is completed through lead L1, switch arm 32, defrost control means 44, line 43, switch arm 33, line 35, fan motor 29, line 36 and lead L2 to energize the fan motor.

The switch arms 49 and 41 in room thermostat 31 are in the position shown in solid line. A circuit is completed through lead L1, switch arm 32, compressor motor 45, switch arm 40, switch arm 41 and lead L2 to energize the compressor motor.

It can thus be seen that when the air conditioning apparatus is operating on the cooling cycle, the compressor 10 is in operation, reversing valve 12 is in the position shown in FIGURE 1, and the fan motor is energized to drive the fans 19 and 21.

When the desired room temperature is attained, switch arm 41 moves to the dotted line position illustrated in FIGURE 2. The circuit is broken to the compressor motor and the compressor motor is deenergized. Though the solenoid 42 is energized at this time, moving the reversing valve 12 to the heating position, this is of no consequence as the compressor is inoperative.

When the indoor temperature drops to a predetermined value indicating the necessity for heat, the switch arm 4-0 moves to the dotted line position illustrated in FIGURE 2. This completes a circuit through lead L1, switch arm 32, compressor motor 45, switch arm 40, switch arm 41 and lead L2 tov energize the compressor motor. Thus the compressor motor, fan motor, and reversing valve remain energized, therefore, the refrigeration system will operate to provide heat. In the event that the refrigerant temperature in line 13 drops to a predetermined value, the strip heater will be energized to supply additional heat.

The resistance heater energizing circuit operates in the following manner: When the outdoor ambient temperature drops, the refrigerant temperature in line 13, which may be considered a part of the suction line, also drops relative to the outdoor temperature. The refrigerant temperature in line 13 is sensed by capillary bulb 26, which is in heat exchange relationship with line 13. At a predetermined refrigerant temperature in line 13, say 36 F. which corresponds to a predetermined outdoor ambient temperature, say 42 F., the bellows 25 will be actuated to close switch 24, thus energizing resistance heater 22. Conversely as the outdoor temperature rises, the corresponding refrigerant temperature in line 13 will also rise and, accordingly, at a predetermined refrigerant temperature, switch 24 will be open deenergizing the resistance heater. The temperatures stated are given by way of illustration and are not to be limitations for it will be apparent that other temperatures might be used.

During operation of the heat pump on the heating cycle, the outdoor heat exchange coil which is located outdoors and which is functioning as an evaporator, often becomes coated with an insulating layer of frost which impedes the etficiency of the heat pump by reducing the heat transfer characteristics of the outdoor coil. Under normal icefree operation of the outdoor coil there is a definite temperature difference between the outside ambient air and the outside coil. This temperature difference permits the defrost control means 44 to remain closed, thus keeping solenoid 42 energized. When ice forms on the outside coil, the temperature of the coil drops. The defrost control switch 44 opens in response to a predetermined difference in temperature between the outside coil and the outside ambient air. When switch 44 opens the solenoid 42 is deenergized. This reverses the refrigerant flow and the outside coil becomes a condenser. The heat dissipated in the outside coil effects the defrosting of this coil.

Since it is also deisrable to stop the fan to facilitate defrosting the outdoor coil 14, the opening of the defrost switch 44 also opens the circuit to the fan motor 20.

If the auxiliary heater 22 were allowed to operate when the fan motor 20 and fan 19 were inoperative, there would be an undesirable concentration of heat in the vicinity of resistance heater 22 and the fusible link would open. If the link 50 burned out, replacement would be necessary. The present invention obviates this problem.

During the defrost portion of the heating cycle of operation the refrigerant line 13 may be considered to be a part of the discharge line. Capillary bulb 26 senses the increasing temperature in the line 13 to open switch 24 and deenergize heater 22. Switch 24 is open within a predetermined time after the deenergization of solenoid 42 to prevent the objections above noted. It can be seen that the thermal responsive element 23 provides means for energizing strip heater 22 in response to a first predetermined condition of refrigerant in line 13 and for deenergizing the strip heater in response to a second predetermined condition of the refrigerant in line 13.

Thus, by the present invention there has been provided an improved control for an air conditioning apparatus employing a resistance heater. The energization and deenergization of auxiliary heater 22 is a function of predetermined conditions of the refrigerant in the line 13 connecting the reversing valve with the outdoor heat exchange coil. The invention is simple and can readily be adapted to self-contained air conditioners.

While I have described a preferred embodiment of the invention, it will be understood that the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

I claim:

1. In a self-contained heat pump, the combination of a compressor, a reversing valve, a discharge line and a suction line connecting said valve with said compressor, an outdoor coil, expansion means, an indoor coil, first conduit means connecting said reversing valve and said outdoor coil, second conduit means connecting said expansion means to said outdoor coil and to said indoor coil, third conduit means connecting said indoor coil and said reversing valve, a heater adapted to supply supplementary heat, a source of electrical current adapted to be connected to said compressor and said heater and control 6 means for energizing said compressor and said heater in response to predetermined temperature conditions, said control means comprising a first control responsive to the temperature of the area to be treated for energizing said compressor, and a second control responsive to the temperature of the refrigerant in said first conduit means and to activation of said first control for energizing said heater.

2. A heat pump as in claim 1 wherein said first control comprises an indoor thermostat.

3. In a heat pump, the combination of a compressor, a reversing valve, a discharge line and a suction line connecting said reversing valve with said compressor, an outdoor coil, expansion means, an indoor coil, first conduit means connecting said reversing valve and said outdoor coil, second conduit means connecting said expansion means to said outdoor coil and to said indoor coil, third conduit means connecting said indoor coil and said reversing valve, means for actuating said reversing valve, means for supplying air over said indoor coil, a heater adapted to supply supplementary heat, a source of electrical current adapted to be connected to the compressor, heater, actuating means, and air supplying means, and control means for energizing said compressor, actuating means, air supplying means, and heater in response to predetermined temperature conditions, said control means comprising a first control responsive to the temperature of the area to be treated to energize said compressor and said air supplying means, a second control responsive to the temperature of the refrigerant in said first conduit means for controlling said heater, said second control energizing said heater upon a predetermined low temperature of said refrigerant, defrost control means operable to temporarily reverse refrigerant flow to supply hot gaseous refrigerant to said outdoor coil, said defrost control means terminating operation of said air supply means, said second control deenergizing said heater upon a predetermined high temperature of said refrigerant gas whereby auxiliary heat is terminated during defrost.

4. In air conditioning apparatus of the type including a refrigeration system operable to selectively heat or cool the air, the combination of a compressor having an inlet and an outlet, motor means for actuating said compressor, first and second heat exchange coils coupled to said compressor inlet and outlet respectively when said apparatus is used for cooling, expansion means coupling the coils to each other, valve means coupled between said coils and said compressor for causing said first and said second coils to be coupled to said compressor, outlet and inlet, respectively when said apparatus is used for heating, a strip heater mounted proximate said first coil for supplementing the heat produced by said coil, a fan for moving air through the first coil and over the strip heater, means for energizing said motor means and said fan, and means for energizing said strip heater connected to said means for energizing said motor means and said fan means responsive to a predetermined temperature differential between the outdoor coil temperature and outdoor temperature to reverse said valve means to cause said first and second coils to be coupled to said compressor inlet to outlet, respectively to effect defrost, said defrost means deenergizing said fan, said strip heater energizing means comprising a thermostat responsive to the temperature of the refrigerant in the coupling between the valve means and the second heat exchange coil, said thermostat being closed during heating operation to energize the strip heater when the temperature of the refrigerant is below a predetermined value and being open to deenergize the strip heater during defrost operation when the temperature of the refrigerant is above a predetermined value.

5. In the method of operating an air-to-air heat pump to condition a room, said heat pump including a reversing valve, an outdoor coil, a fan, auxiliary heating means, and a compressor, the steps which consist in energizing the compressor and fan to cool on a predetermined high temperature of the room, energizing the reversing valve,

compressor and fan to heat upon a predetermined low temperature of the room, energizing the auxiliary heating means upon a first predetermined temperature of the refrigerant in the connection between the reversing valve and the outdoor coil, deenergizing the reversing valve and the fan to defrost the outside coil upon a predetermined outdoor coil-outdoor temperature differential, and deenergizing the auxiliary heating means during defrost upon a second predetermined temperature of the refrigerant in the connection between the reversing valve and the outdoor coil.

6. In a heat pump, the combination of a compressor, a fan, an auxiliary heater, a reversing valve, an outdoor coil, an expansion means, and an indoer coil interconnected to form a reverse cycle refrigeration system, means for energizing said reversing valve, compressor and fan upon a predetermined room temperature to heat, means for energizing said auxiliary heater upon a first predetermined temperature of the refrigerant in the connection References Cited bythe Examiner UNITED STATES PATENTS 2,847,190 8/58 Slattery et al. 165--17 2,934,323 4/60 Burke 16512 2,969,959 1/61 Kuhn et a1. 165-17 2,995,345 8/61 Manetta et a1. 165-29 CHARLES SUKALO, Primary Examiner.

HERBERT L. MARTIN, PERCY L. PATRICK,

Examiners. 

5. IN THE METHOD OF OPERATING AN AIR-TO-AIR HEAT PUMP TO CONDITION A ROOM, SAID HEAT PUMP INCLUDING A REVERSING VALVE, AN OUTDOOR COIL, A FAN AUXILIARY HEATING MEANS, AND A COMPRESSOR, THE STEPS WHICH CONSIST IN ENERGIZING THE COMPRESSOR AND FAN TO COOL ON A PREDETERMINED HIGH TEMPERATURE OF THE ROOM, ENERGIZING THE REVERSING VALVE, COMPRESSOR AND FAN TO HEAT UPON A PREDETERMINED LOW TEMPERATURE OF THE ROOM, ENERGIZING THE AUXILIARY HEATING MEANS UPON A FIRST PREDETERMINED TEMPERATURE OF THE REFRIGERANT IN THE CONNECTION BETWEEN THE REVERSING VALVE AND THE OUTDOOR COIL, DEENERGIZING THE REVERSING VALVE AND THE FAN TO DEFROST THE OUTSIDE COIL UPON A PREDETERMINED OUTDOOR COIL-OUTDOOR TEMPERATURE DIFFERENTIAL, AND DEENENERGIZING THE AUXILIARY HEATING MEANS DURING DEFROST UPON A SECOND PREDETERMINED TEMPERATURE OF THE REFRIGARENT IN THE CONNECTION BETWEEN THE REVERSING VALVE AND THE OUTDOOR COIL. 